(a) Field of the Invention
This invention relates to novel compounds classified in the field of organic chemistry as phenothiazines, useful as color-forming substances, particularly in the art of electrochromic recording; to electrochromic recording systems containing said compounds; and to processes for preparing said compounds.
(b) Information Disclosure Statement
Several classes of organic compounds of widely diverse structural types are known to be useful as colorless precursors for electrochromic recording. Among the more important classes, there may be named leuco-type dyestuffs such as: phthalides, for example, crystal violet lactone, Malachite green lactone; fluorans, for example, 3-diethylamino-5,7-dimethylfluoran; and indolinobenzospiropyrans, for example, 1,3,3-trimethyl-6'-chloro-8'-methoxyindolino-benzospiropyrans. Also utilized as colorless precursors for electrochromic recording, either alone or in admixture with the leuco compounds indicated above, are substances known as redox indicators. The redox indicator which becomes colored in situ in the electrochromic recording process also is generally a leuco compound. Among the types of compounds which are applicable as redox indicators are phenothiazines, for example, leuco methylene blue and benzoyl leuco methylene blue. Other specific indicators are Leucoethyl Nile Blue, Leucomethyl Capyrl Blue and Leucosafranine T. Typical of the many such electrochromic recording systems taught in the prior art are those described in U.S. Pat. Nos. 3,726,769, 3,871,972, 3,864,684, 4,017,366, 4,133,933, and Pat. Re. 29,427 which issued Apr. 10, 1973, Mar. 18, 1975, Feb. 4, 1975, Apr. 12, 1977, Jan. 9, 1979, and Oct. 4, 1977, respectively. The methods for electrochromic recording taught in the prior art have many variations. Basically, a sheet of paper is coated or treated on one or both sides with a coating formulation containing at least one colorless color-forming (leuco) compound. Electrical current is then selectively applied to the coated side of the paper by some means, for example, a stylus or a printing head to which an electrical potential can be applied. The application of the current causes an electrochromic reaction involving the leuco compound to produce a visible image corresponding to the design traced by the stylus or that of the printing head.
The following items to date appear to constitute the most relevant prior art with regard to the instant invention.
U.S. Pat. No. 2,909,520, issued Oct. 20, 1959, discloses compounds having the formula ##STR1## in which R is a phenyl or naphthyl groups substituted with one or more of the following moieties: alkyl, alkoxy, halo, nitro, haloalkyl, alkoxycarbonyl, phenyl, and phenylalkoxy. These compounds are disclosed as being useful as blue color formers in carbonless carbon papers, i.e., carbonless duplicating systems.
Mariga and Oda in Kogyo Kagaku Zasshi 67 (7), 1050-4 (1964) (C.A. 62 2852b) describe the preparation and properties of acylated methylene blue having the structural formula ##STR2## in which R represents an alkyl or a substituted phenyl moiety. The compounds are disclosed as being useful in pressure-sensitive carbonless duplicating systems.
U.S. Pat. No. 4,309,255, issued Jan. 5, 1982, discloses and claims a phenothiazine having the structural formula ##STR3## which is disclosed as being useful as a blue color former in electrochromic recording paper.